1. Field of the Invention
The present invention relates to a frame structure used for a vehicle body.
2. Description of the Prior Art
In general, the front frame structure of a vehicle body is composed of right and left front frames and a lower radiator frame. Here, each of the right and left front frames is formed into a box-shaped cross section so as to extend in the longitudinal (front to rear) direction of the vehicle along the inner side of each of right and left front wheel aprons both constructing side walls of an engine compartment. On the other hand, the lower radiator frame is used to join the front ends of the right and left front frames. Further, the rear ends of the right and left front frames are usually butt-joined to a toe board for partitioning the engine compartment from a vehicle compartment.
In the conventional vehicle front frame structure as described above, in case of vehicle collision, it is necessary to effectively absorb shock energy by allowing the two front frames to be deformed in buckling mode. For this purpose, conventionally, in order to allow the front frames to be deformed in buckling mode in case of vehicle collision, a measure has been adopted to form a plurality of bead portions extending in the vertical direction on at least one side surface of the box-shaped front frame, as disclosed in Japanese Patent Application Laid-Open Publication No. 3-94137 or in Japanese Utility Model Application Laid-Open Publication No. 3-16580, for instance.
Here, it is basically ideal to form each of the two front frames as a straight part extending in the front to rear direction, in the practical vehicle design. However, the shape of the front frames is severely restricted due to various parts to be arranged in the engine compartment, so that the front frames 1 are inevitably formed with a bent portion 1a roughly midway portion thereof, as shown in FIG. 4. Further, in FIG. 4, each front frame 1 is fixed between a front wheel apron 2 and a toe board 3, and the front frame 1 is further formed with a plurality of vertical bead portions 4.
In the conventional front frame structure as described above, having a plurality of bead portions 4 extending in the vertical direction and formed on the side surface of the front frame with the bent portion 1a formed roughly midway thereof, in case a collision load F is applied to the front end of the front frame 1 and thereby a bending moment M1 is generated at the bent portion 1a, the vertical bead portions 4 cannot effectively suppress the bending deformation at the bent portion 1a, depending on the way of arrangement of the bead portions, with the result that there exists a problem in that collision energy cannot be absorbed effectively. In other words, in the conventional front frames, there exists a problem in that it is difficult to determine how the vertical bead portions 4 are arranged.